Radio communication system, base station, relay station, and radio communication method

ABSTRACT

A base station which is able to perform radio communications with a relay station and a mobile station, the base station includes a transmitter configured to transmit radio signals to the relay station in downlink backhaul subframes, and to limit transmission of radio signals to the relay station in subframes other than the downlink backhaul subframes; and a controller configured to allow, when performing a random access procedure to the relay station, the transmitter to transmit a message of the random access procedure even in the subframes other than the downlink backhaul subframes.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/793,110, filed on Jul. 7, 2015, which is a continuation of U.S.application Ser. No. 13/753,176, filed on Jan. 29, 2013, which issued asU.S. Pat. No. 9,113,466 on Aug. 18, 2015, which is a continuation ofInternational Patent Application number PCT/JP2010/063748 filed Aug. 13,2010 in Japan, the entire contents of each are herein incorporated byreference.

FIELD

The embodiments discussed herein are related to a radio communicationsystem, a base station, a relay station, and a radio communicationmethod.

BACKGROUND

At present, radio communication systems such as a cell-phone system anda radio MAN (Metropolitan Area Network) are widely used. For attaining afurther speeding up and large capacity of radio communication, livelydiscussion is continuously performed about a next generation radiocommunication technology. For example, the 3GPP (3rd GenerationPartnership Project), which is one of international standardizationorganizations, proposes a standard referred to as LTE (Long TermEvolution), and a standard referred to as LTE-A (Long TermEvolution-Advanced) that is an evolution of LTE (see, for example, 3rdGeneration Partnership Project, “Requirements for further advancementsfor Evolved Universal Terrestrial Radio Access (E-UTRA)”, 3GPP TR 36.913V8.0.1, 2009-03).

In a radio communication system including a base station and a mobilestation, a relay station which relays radio communication may beprovided between the base station and the mobile station. By providing arelay station, an area (dead spot) in which radio communication isdifficult due to radio propagation blocking caused by buildings iscovered, a range of a cell covered by a base station is expanded, andcommunication throughput is improved.

However, in a relay station, interference (which may be referred to asself-interference) may occur between a transmission signal of its ownstation and a reception signal. Suppose, for example, that a frequencyband used between a base station and a relay station and a frequencyband used between the relay station and a mobile station are overlappedwith each other. In this case, a radio signal transmitted to the mobilestation comes into a receiver of the relay station, and as a result aradio signal may not correctly be received from the base station. Tocope with the problem, the relay station is proposed to be controlled insuch a manner that reception of a radio signal from the base station andtransmission of a radio signal to the mobile station are not performedat the same time (see, for example, section 9. 3 of 3rd GenerationPartnership Project, “Feasibility study for Further advancements forE-UTRA”, 3GPP TR 36.912 V9.0.0, 2009-09).

Another radio communication system including a base station and a mobilestation may provide a configuration in which a procedure of randomaccess from the mobile station to the base station is specified. In therandom access, the mobile station accesses the base station withoutbeing dedicatedly allocated a radio resource by the base station (see,for example, section 10. 1. 5 of 3rd Generation Partnership Project,“Evolved Universal Terrestrial Radio Access (E-UTRA) and EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN); Overalldescription”, 3GPP TS 36.300 V9.3.0, 2010-03).

As a random access preamble (which may be referred to as Msg 1), forexample, the mobile station transmits to the base station a signalsequence selected from among a plurality of candidates through apredetermined random access channel. The base station, having receivedthe Msg 1, transmits as a response a random access response (which maybe referred to as Msg 2). Note that at this time, the base station doesnot recognize the transmission source device of the Msg 1. The mobilestation, having received the Msg 2, transmits to the base station amessage (which may be referred to as Msg 3) including the identifier ofits own station. The base station, having received the Msg 3, transmitsto the mobile station a message (which may be referred to as Msg 4) as aresponse.

Here, an interval until the base station sends back the Msg 2 fromreception of the Msg 1 and an interval until the base station sends backthe Msg 4 from reception of the Msg 3 are not fixed, and preferably staywithin a predetermined allowable range. Based on this flexibility, thebase station may perform scheduling and efficiently transmit the Msg 2and Msg 4. While the base station may transmit the Msg 2 or Msg 4, themobile station monitors a radio signal from the base station and detectsthe Msg 2 or Msg 4 (see, for example, section 5. 1 of 3rd GenerationPartnership Project, “Evolved Universal Terrestrial Radio Access(E-UTRA); Medium Access Control (MAC) protocol specification”, 3GPP TS36.321 V9.3.0, 2010-06).

Think of a radio communication system which includes a base station, arelay station, and a mobile station, and in which the relay stationperforms random access to the base station. At this time, there arises aproblem that how the base station and the relay station preferablyperform a random access procedure. Specifically, in the conventionalrandom access, timing at which a base station may send back a messagevaries. If the message is sent back at timing at which the relay stationtransmits a radio signal to the mobile station, the relay station maynot correctly receive the message due to self-interference.

SUMMARY

According to an aspect, there is provided a radio communication systemwhich includes: a base station; a relay station which performs wirelesscommunications with the base station; and a mobile station whichperforms wireless communications with the base station or relay station,wherein: the relay station includes: a first radio communication unitwhich transmits a first message about random access to the base stationand which receives from the base station a radio signal including asecond message about the random access; and a first controller whichlimits reception of a radio signal from the base station at timing atwhich a radio signal is transmitted to the mobile station; and the basestation includes: a second radio communication unit which receives thefirst message and transmits the second message; and a second controllerwhich controls transmission timing of the second message based onwhether a transmission source of the received first message is the relaystation.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a radio communication system according to a firstembodiment;

FIG. 2 illustrates a radio communication system according to a secondembodiment;

FIG. 3 illustrates a structure example of a radio frame;

FIG. 4 illustrates a use example of a radio resource;

FIG. 5 is a sequence diagram illustrating a procedure example of randomaccess;

FIG. 6 is a block diagram illustrating a base station;

FIG. 7 is a block diagram illustrating a relay station;

FIG. 8 is a block diagram illustrating a mobile station;

FIG. 9 is a flowchart illustrating a process of a base station accordingto a second embodiment;

FIG. 10 is a flowchart illustrating a process of a relay stationaccording to a second embodiment;

FIG. 11 is a flowchart illustrating a process of a mobile stationaccording to a second embodiment;

FIG. 12 illustrates a random access example according to a secondembodiment;

FIG. 13 is a flowchart illustrating a process of a base stationaccording to a third embodiment;

FIG. 14 is a flowchart illustrating a process of a relay stationaccording to a third embodiment;

FIG. 15 is a flowchart illustrating a process of a mobile stationaccording to a third embodiment;

FIG. 16 illustrates a random access example according to a thirdembodiment;

FIG. 17 illustrates another random access example according to a thirdembodiment;

FIG. 18 is a flowchart illustrating a process of a base stationaccording to a fourth embodiment;

FIG. 19 is a flowchart illustrating a process of a relay stationaccording to a fourth embodiment;

FIG. 20 illustrates a random access example according to a fourthembodiment;

FIG. 21 illustrates another random access example according to a fourthembodiment;

FIG. 22 is a flowchart illustrating a process of a base stationaccording to a fifth embodiment;

FIG. 23 is a flowchart illustrating a process of a relay stationaccording to a fifth embodiment;

FIG. 24 illustrates a random access example according to a fifthembodiment;

FIG. 25 is a flowchart illustrating a process of a base stationaccording to a sixth embodiment;

FIG. 26 is a flowchart illustrating a process of a relay stationaccording to a sixth embodiment;

FIG. 27 illustrates a random access example according to a sixthembodiment;

FIG. 28 is a flowchart illustrating a process of a base stationaccording to a seventh embodiment;

FIG. 29 is a flowchart illustrating a process of a relay stationaccording to a seventh embodiment; and

FIG. 30 illustrates a random access example according to a seventhembodiment.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail below with reference to the accompanying drawings, wherein likereference numerals refer to like elements throughout.

First Embodiment

FIG. 1 illustrates a radio communication system according to a firstembodiment. The radio communication system according to the firstembodiment includes a base station 10, a relay station 20, and a mobilestation 30. Examples of the mobile station 30 include a cellular phoneand a personal digital assistant device. The relay station 20 may be amobile radio relay station or a fixed radio relay station. The mobilestation 30 performs wireless communications with the base station 10 orrelay station 20. The relay station 20 performs random access (RA) tothe base station 10 and establishes a connection, thus relaying datacommunication between the base station 10 and the mobile station 30.

The base station 10 includes a radio communication unit 11 and acontroller 12. The radio communication unit 11 receives a first message(message #1) about random access and transmits a second message (message#2) about the random access. Examples of the message #1 include a Msg 1and a Msg 3, and examples of the message #2 include a Msg 2 and a Msg 4.The controller 12 determines whether a transmission source of themessage #1 received by the radio communication unit 11 is the relaystation 20. Based on whether the transmission source is the relaystation 20, the controller 12 then controls timing at which the radiocommunication unit 11 transmits the message #2.

The relay station 20 includes a radio communication unit 21 and acontroller 22. The radio communication unit 21 performs wirelesscommunications with the base station 10. During the random access, theradio communication unit 21 transmits the message #1 to the base station10, and receives the message #2 from the base station 10. The controller22 controls timing of radio communication so that self-interference willnot occur between a radio signal received from the base station 10 and aradio signal transmitted to the mobile station 30. Concretely, at timingat which a radio signal is transmitted to the mobile station 30, theradio communication unit 21 limits reception of a radio signal from thebase station 10 (e.g., stops a receiving circuit). In the radio signaltransmitted to the mobile station 30 by the relay station 20, an RS(Reference Signal) used for a measurement of communication qualitythrough the mobile station 30 is included.

Here, in the case where the message #1 is the Msg 1, examples of themethod for determining a transmission source of the message #1 throughthe controller 12 include a method based on a signal sequence includedin the message #1 and a method based on timing at which the message #1is received. In the former method, a signal sequence for the relaystation and a signal sequence for the mobile station are prepared andthe radio communication unit 21 generates the message #1 by using thesignal sequence for the relay station. In the case where another relaystation is present in the radio communication system, the relay station20 may use the signal sequence for the relay station shared with theanother relay station. In the latter method, a RACH (random accesschannel) for the relay station and a RACH for the mobile station areconfigured separately and the radio communication unit 21 transmits themessage #1 through the RACH for the relay station.

In the case where a transmission source of the message #1 is the relaystation 20 (or another relay station) or the mobile station 30 (oranother mobile station), the controller 12 then changes an algorithm fordetermining transmission timing of the message #2. In the former case,the controller 12 selects timing at which the relay station 20 does notlimit reception of a radio signal. About the timing at which data iscapable of being transmitted from the base station 10 to the relaystation 20, for example, when some agreements have been reached betweenboth the stations, the controller 12 selects the timing according to theagreements. On the other hand, in the latter case, the controller 12performs scheduling and selects arbitrary timing within an allowableperiod.

According to the proposed radio communication system of the firstembodiment, the relay station 20 limits reception of a radio signal fromthe base station 10 at the timing at which a radio signal is transmittedto the mobile station 30. The relay station 20 further transmits themessage #1 to the base station 10. The base station 10 determineswhether a transmission source of the message #1 is the relay station 20,and transmits the message #2 at timing determined according todetermination results. The relay station 20 receives the message #2 fromthe base station 10.

As a result, the radio communication system smoothly performs randomaccess from the relay station 20 to the base station 10. Specifically,the relay station 20 limits the reception so that self-interference willnot occur between a radio signal received from the base station 10 and aradio signal transmitted to the mobile station 30. When a transmissionsource of the message #1 is not the mobile station 30 but the relaystation 20, the base station 10 determines transmission timing of themessage #2 in consideration of the limitation of the reception timing ofthe relay station 20. Therefore, the radio communication systemsuppresses the possibility that the relay station 20 cannot receive themessage #2 in a normal way.

In second to seventh embodiments described below, there is included anexample of a radio communication system including a base station, arelay station, and a mobile station in conformity to the LTE or LTE-A.

Second Embodiment

FIG. 2 illustrates a radio communication system according to a secondembodiment. The radio communication system according to the secondembodiment includes a base station 100, relay stations 200 and 200 a,and mobile stations 300 and 300 a. In the following description, supposemainly that the mobile station 300 performs data communication with thebase station 100 via the relay station 200 and the mobile station 300 adirectly performs data communication with the base station 100.

The base station 100 is a radio communication apparatus which performswireless communications with the relay stations 200 and 200 a, and themobile station 300 a. The base station 100 is connected to a hoststation (not illustrated) via a wired line. The base station 100receives data from the host station, and transfers it to the relaystations 200 and 200 a, and the mobile station 300 a through a downlink(DL). On the other hand, through an uplink (UL), the base station 100receives data from the relay stations 200 and 200 a, and the mobilestation 300 a, and transfers it to the host station.

The relay station 200 is a radio communication apparatus which relaysdata communication between the base station 100 and the mobile station300. Through the DL, the relay station 200 receives data from the basestation 100 and transfers it to the mobile station 300. On the otherhand, through the UL, the relay station 200 receives data from themobile station 300 and transfers it to the base station 100. In asimilar fashion, the relay station 200 a also relays data communication.The relay stations 200 and 200 a may be mobile radio relay stations orfixed radio relay stations.

Here, the relay stations 200 and 200 a correspond to a so-called Type 1of relay station. Specifically, the relay stations 200 and 200 a performprotocol processing up to a layer 3, and behave to the mobile stations300 and 300 a in the same manner as in the base station 100. From themobile stations 300 and 300 a, a cell apart from that provided by thebase station 100 is viewed to be provided by the relay stations 200 and200 a. A frequency band used for radio communication between the basestation and the relay station is at least partially overlapped with afrequency band used for radio communication between the relay stationand the mobile station.

The mobile stations 300 and 300 a are radio terminal apparatus whichcommunicate with the base station 100. The mobile stations 300 and 300 acommunicate with the base station 100 via the relay stations 200 and 200a. Examples of the mobile stations 300 and 300 a include a cellularphone and a personal digital assistant device. Through the DL, themobile station 300 receives data from the relay station 200. Through theUL, on the other hand, the mobile station 300 transmits data to therelay station 200.

For radio communication through the DL, an OFDMA (Orthogonal FrequencyDivision Multiple Access) is used, and for radio communication throughthe UL, an SC-FDMA (Single Carrier Frequency Division Multiple Access)is used. Further, a base station may be called a BS (Base Station), arelay station may be called an RN (Relay Node) or an RS (Relay Station),and a mobile station may be called an MS (Mobile Station) or a UE (UserEquipment).

FIG. 3 illustrates a structure example of a radio frame. Through each ofthe DL and UL, the radio frame as illustrated in FIG. 3 is transmittedand received between a base station and a relay station as well asbetween a relay station and a mobile station. In the second embodiment,an FDD (Frequency Division Duplex) is used as a duplex system. Note thata TDD (Time Division Duplex) may be used.

A radio frame with a width of 10 msec includes ten subframes (subframes#0 to #9) with a width of 1 msec. Each subframe includes two slots (afirst-half slot and a second-half slot) with a width of 0.5 msec.Scheduling of data or control signals is performed in units ofsubframes. A radio resource of the subframe is segmentalized in thefrequency direction or in the time direction for management. A minimumunit in the frequency direction is a sub-carrier and a minimum unit inthe time direction is a symbol. The number of symbols included in thesubframe may be different depending on a type of subframes.

FIG. 4 illustrates an example of radio resource usage. A communicationchannel is provided on a DL subframe and an UL subframe transmitted andreceived by the relay stations 200 and 200 a.

In the DL subframe, several symbols (one to three symbols) of the headare an area for control and remaining symbols are an area for data. Onthe area for control, a PDCCH (Physical Downlink Control Channel) fortransmitting a physical control signal is provided. On the area fordata, a PBCH (Physical Broadcast Channel) for transmitting broadcastinformation and an R-PDCCH (Relay Physical Downlink Control Channel) fortransmitting control data on a relay are provided. On the UL subframe, aPRACH (Physical Random Access Channel) for transmitting a random accesspreamble is provided.

On the DL subframe, a reference signal being a pilot signal istransmitted in both of the areas for control and data. While DL datacommunication is not performed, a reference signal is transmitted. Themobile station 300 measures a reception power level or radio quality byusing a reference signal.

Here, the relay stations 200 and 200 a receive data from the basestation 100 and configure a subframe (DL backhaul) which does not carrydata to a subordinate mobile station. In signals in which transmissionis stopped, a reference signal is also included. Note that in the areafor control, the relay stations 200 and 200 a are allowed to receivedata from the base station 100 and transmit data to the subordinatemobile station at the same time. In other words, the relay stations 200and 200 a may stop transmitting data in both of the areas for controland data, or only in the area for data.

For example, the DL backhaul is configured so that the DL subframe ofthe relay stations 200 and 200 a may be an MBSFN (Multimedia Broadcastmulticast service Single Frequency Network) subframe. The MBSFN subframeis a subframe in which the base station 100 normally performs MBSFNtransmission. The MBSFN transmission is used in the case where aplurality of transmitting stations concertedly transmit data of the samecontent at the same timing by using the same frequency and modulationscheme. In the second embodiment, in the radio communication systemincluding the relay stations 200 and 200 a, the MBSFN subframe is usedfor configuring a DL backhaul subframe of the relay stations 200 and 200a. Through the process, as illustrated in FIG. 4, for example, since therelay stations 200 and 200 a do not transmit a reference signal in thearea for data of the MBSFN subframe, self-interference does not occureven if the relay stations 200 and 200 a receive data in the area.

The relay stations 200 and 200 a further transmit data to the basestation 100 and configure a subframe (UL backhaul) in which data is notreceived from a subordinate mobile station. Timing for the DL backhauland timing for the UL backhaul may be the same or different from eachother.

The relay stations 200 and 200 a configured with the UL backhaul do notgive data transmission permissions (UL grant) before a predeterminedtime (e.g., four subframes) from the UL backhaul. As a result, thesubordinate mobile stations do not transmit data in the UL backhaul.Further, the relay stations 200 and 200 a do not transmit data to thesubordinate mobile stations before a predetermined time from the ULbackhaul. As a result, the subordinate mobile stations do not transmitan ACK (Acknowledgement)/NACK (Negative Acknowledgement) in the ULbackhaul.

Note that the relay stations 200 and 200 a control timing at which thesubordinate mobile stations transmit data as described above. Therefore,even in every subframe except the predetermined UL backhaul, the relaystations 200 and 200 a can stop receiving data from the subordinatemobile station and transmit data to the base station 100 throughscheduling.

In addition, timing for the backhaul has been agreed between the basestation 100 and the relay stations 200 and 200 a. The relay stations 200and 200 a may determine the timing and notify the base station 100 ofthe timing. Or, alternatively, the base station 100 may determine thetiming and notify the relay stations 200 and 200 a of the timing. Thetiming for the backhaul may be different between the relay stations 200and 200 a. The relay stations 200 and 200 a broadcast informationindicating the timing for the backhaul. The mobile station 300recognizes the timing based on the broadcast information received fromthe relay station 200.

FIG. 5 is a sequence diagram illustrating a procedure example of therandom access. Here, the mobile station 300 a performs random access tothe base station 100. The procedure of the random access illustrated inFIG. 5 includes the following steps:

(Step S1) The mobile station 300 a selects one signal sequence fromamong candidates of a plurality of signal sequences and transmits it asa random access preamble (Msg 1) through the PRACH. Hereinafter, therandom access preamble may be referred to simply as a preamble.

(Step S2) After detecting Msg 1, the base station 100 transmits a randomaccess response (Msg 2). The Msg 2 is transmitted within a predeterminedperiod. More specifically, the base station 100 transmits the Msg 2within a period of A pieces of subframes counted after three subframesfrom the subframe in which the Msg 1 is received. A value of A ispreviously set to any of 2, 3, 4, 5, 6, 7, 8, and 10.

(Step S3) Within the period in which the Msg 2 may be transmitted, themobile station 300 a monitors a received signal from the base station100. After detecting the Msg 2, the mobile station 300 a transmits amessage (Msg 3) called a scheduled transmission to the base station 100.In the Msg 3, an identifier of the mobile station 300 a is included.

(Step S4) The base station 100 receives the Msg 3 from the mobilestation 300 a and transmits a message (Msg 4) called ContentionResolution to the mobile station 300 a. The Msg 4 is transmitted withina predetermined period. More specifically, the base station 100transmits the Msg 4 within B pieces of subframes counted from thesubframe in which the Msg 3 is received. A value of B is previously setto any of 8, 16, 24, 32, 40, 48, 56, and 64. Within the period in whichthe Msg 4 may be transmitted, the mobile station 300 a monitors areceived signal from the base signal 100.

Incidentally, a clue (RA trigger) in which random access is performedincludes the following.

(1) Abnormality is detected in a connection between the base station 100and the mobile station 300 a. The abnormality in the connection includesa case where a timer T310 is time out as described in 3rd GenerationPartnership Project, “Evolved Universal Terrestrial Radio Access(E-UTRA); Radio Resource Control (RRC); Protocol specification”, 3GPP TS36.331 V9.2.0, 2010-03 and a case of failing in retransmission controlof data in an RLC (Radio Link Control) layer.

(2) The mobile station 300 a receives an instruction of starting ahandover from a base station as a handover source, and accesses a basestation as a handover destination.

(3) The mobile station 300 a fails in access to the base station 100 byusing a scheduling request scheme. The scheduling request scheme is anaccess scheme in which the mobile station 300 a transmits a schedulingrequest to the base station 100 by using a radio resource for controldata and receives an allocation of a radio resource for datatransmission.

(4) The mobile station 300 a fails in data transmission to the basestation 100 by using a contention based uplink transmission method. Thecontention based uplink transmission method is a method in which themobile station 300 a transmits data to the base station 100 by using aradio resource shared by a plurality of mobile stations. Failure in thedata transmission may be caused by the contention. The contention baseduplink transmission method is described, for example, in a collection ofwriting about 3GPP (R2-093812, “Contention based uplink transmission”).

(5) The mobile station 300 a fails in security authentication.

(6) The mobile station 300 a fails in reconfiguration of a radioresource, namely, reconfiguration of RRC (Radio Resource Control)connection. Reconfiguration of the RRC connection is described, forexample, in a section 5. 3. 5. 5 of 3rd Generation Partnership Project,“Evolved Universal Terrestrial Radio Access (E-UTRA); Radio ResourceControl (RRC); Protocol specification”, 3GPP TS 36.331 V9.2.0, 2010-03.

Even at the time of the random access from the relay stations 200 and200 a to the base station 100, the Msg 1 to Msg 4 are transmitted in thesame manner as in the random access from the mobile station 300 a to thebase station 100. Note that in the case of the relay stations 200 and200 a, transmission timing of the Msg 2 and Msg 4 is different from thatof the mobile station 300 a.

FIG. 6 is a block diagram illustrating the base station. The basestation 100 includes a radio communication unit 110, a wiredcommunication unit 120, a data processing unit 130, and a controller140.

The radio communication unit 110 is a radio interface which performswireless communications with the relay stations 200 and 200 a, and themobile station 300 a. The radio communication unit 110 performs signalprocessing including demodulation and decoding to the received radiosignal, and extracts data and a control signal. The radio communicationunit 110 further detects a preamble transmitted through the PRACH. Theradio communication unit 110 supplies data to be transferred to a hoststation to the data processing unit 130. On the other hand, the radiocommunication unit 110 obtains data from the data processing unit 130and generates a control signal based on an instruction from thecontroller 140. The radio communication unit 110 then performs signalprocessing including coding and modulation to data and a control signal,and outputs a radio signal.

The wired communication unit 120 is a communication interface whichperforms wired communication with the host station. The wiredcommunication unit 120 receives data addressed to the mobile stations300 and 300 a from the host station, and supplies it to the dataprocessing unit 130. On the other hand, the wired communication unit 120converts the data obtained from the data processing unit 130 into apacket form of a wired network and transmits it to the host station.

The data processing unit 130 obtains data to be transferred to the hoststation from the radio communication unit 110 and supplies it to thewired communication unit 120. On the other hand, the data processingunit 130 obtains data addressed to the mobile stations 300 and 300 afrom the wired communication unit 120 and maps data to a radio frameunder the control of the controller 140, thus supplying it to the radiocommunication unit 110.

The controller 140 controls processes of the radio communication unit110, wired communication unit 120, and data processing unit 130. Thecontroller 140 has a data plane unit 150 and a control plane unit 160.The data plane unit 150 controls transmission and reception of databetween its own station and any of the relay stations 200 and 200 a andthe mobile station 300 a. The control plane unit 160 controlstransmission and reception of a control signal between its own stationand any of the relay stations 200 and 200 a and the mobile station 300a.

Namely, the control plane unit 160 obtains the control signal extractedby the radio communication unit 110 and performs communication controlaccording to the control signal. The control plane unit 160 furthernotifies the radio communication unit 110 of the transmitted controlsignal. The control plane unit 160 has a preamble management unit 161,an RA slot management unit 162, and a backhaul controller 163.

The preamble management unit 161 manages candidates of the preamblesused for random access. When a preamble for the relay station and apreamble for the mobile station are distinguished, the preamblemanagement unit 161 determines whether the preamble detected by theradio communication unit 110 is one for the relay station or one for themobile station.

The RA slot management unit 162 manages a slot (RA slot) in which thePRACH is configured. When an RA slot for the relay station and an RAslot for the mobile station are distinguished, the RA slot managementunit 162 determines whether a slot in which a preamble is detected bythe radio communication unit 110 is one for the relay station or one forthe mobile station. Further, the RA slot management unit 162 maydynamically configure an RA slot according to occurrence conditions ofan RA trigger or configuration status of a DL backhaul of the relaystations 200 and 200 a.

The backhaul controller 163 manages backhauls of the relay stations 200and 200 a, and controls timing of transmission and reception of a radiosignal. When a random access source is the relay station, the backhaulcontroller 163 refers to configuration status of the DL backhaul of therelay stations 200 and 200 a, and determines timing for transmitting theMsg 2 or Msg 4.

FIG. 7 is a block diagram illustrating the relay station. The relaystation 200 includes radio communication units 210 and 220, a scheduler230, and a controller 240. The relay station 200 a is also deployedthrough the same block structure as that of the relay station 200.

The radio communication unit 210 is a radio interface which performswireless communications with the base station 100. The radiocommunication unit 210 performs signal processing including demodulationand decoding to the received radio signal, and extracts data or acontrol signal. The radio communication unit 210 supplies data addressedto the mobile station 300 to the scheduler 230. On the other hand, theradio communication unit 210 obtains data from the scheduler 230 andgenerates a control signal or a preamble based on the instruction fromthe controller 240. The radio communication unit 210 then performssignal processing including coding and modulation and outputs a radiosignal.

The radio communication unit 220 is a radio interface which performswireless communications with the mobile station 300. The radiocommunication unit 220 performs signal processing including demodulationand decoding to the received radio signal and extracts data or a controlsignal. The radio communication unit 220 supplies data to be transferredto the base station 100 to the scheduler 230. On the other hand, theradio communication unit 220 obtains data from the scheduler 230, andgenerates a control signal or a reference signal based on theinstruction from the controller 240. The radio communication unit 220then performs signal processing including coding and modulation, andoutputs a radio signal.

The scheduler 230 schedules transfer of data from the base station 100to the mobile station 300 and transfer of data from the mobile station300 to the base station 100. Namely, the scheduler 230 maps dataaddressed to the mobile station 300 obtained from the radiocommunication unit 210 to a DL radio frame, and supplies it to the radiocommunication unit 220. On the other hand, the scheduler 230 maps dataaddressed to the base station 100 obtained from the radio communicationunit 220 to an UL radio frame, and supplies it to the radiocommunication unit 210.

The controller 240 controls processes of the radio communication units210 and 220 and the scheduler 230. The controller 240 has a data planeunit 250 and a control plane unit 260.

The data plane unit 250 controls transmission and reception of databetween its own station and any of the base station 100 and the mobilestation 300. The data plane unit 250 has a scheduler controller 251. Thescheduler controller 251 manages a method for scheduling the scheduler230.

The control plane unit 260 controls transmission and reception of acontrol signal between its own station and any of the base station 100and the mobile station 300. Specifically, the control plane unit 260obtains the control signal extracted by the radio communication units210 and 220, and performs communication control according to the controlsignal. The control plane unit 260 further notifies the radiocommunication units 210 and 220 of the transmitted control signal. Thecontrol plane unit 260 has a preamble management unit 261, an RAtransmission management unit 262, and a backhaul controller 263.

The preamble management unit 261 manages candidates of the preamblesused in the random access, and selects a preamble used in the Msg 1during the random access to the base station 100. When the preamble forthe relay station and the preamble for the mobile station aredistinguished, the preamble management unit 261 selects the preamble forthe relay station.

The RA transmission management unit 262 grasps an RA slot and selects anRA slot used to transmit the Msg 1 during the random access to the basestation 100. When the RA slot for the relay station and the RA slot forthe mobile station are distinguished, the RA transmission managementunit 262 selects the RA slot for the relay station.

The backhaul controller 263 manages a backhaul of its own station andcontrols timing of transmission and reception of a radio signal.Particularly, at least in the area for data of the DL backhaul, thebackhaul controller 263 does not transmit data or a reference signal tothe mobile station 300. In addition to the backhaul used in normal datacommunication, the backhaul controller 263 may configure a temporarybackhaul during the random access.

FIG. 8 is a block diagram illustrating the mobile station. The mobilestation 300 includes a radio communication unit 310, a data processingunit 320, and a controller 330. The mobile station 300 a is alsodeployed by using the same block structure as that of the mobile station300.

The radio communication unit 310 is a radio interface which performswireless communications with the relay station 200 or base station 100.The radio communication unit 310 performs signal processing includingdemodulation and decoding to the received radio signal, and extractsdata or a control signal. The radio communication unit 310 supplies theextracted data to the data processing unit 320. On the other hand, theradio communication unit 310 obtains data from the data processing unit320 and generates a control signal based on the instruction from thecontroller 330. The radio communication unit 310 then performs signalprocessing including coding and modulation, and outputs a radio signal.

The data processing unit 320 generates data to be transmitted to therelay station 200 or base station 100 and supplies it to the radiocommunication unit 310. On the other hand, the data processing unit 320obtains data addressed to its own station from the radio communicationunit 310 and performs a process according to a type of data.

The controller 330 controls processes of the radio communication unit310 and the data processing unit 320. The controller 330 has a dataplane unit 340 and a control plane unit 350. The data plane unit 340controls transmission and reception of radio data. The control planeunit 350 controls transmission and reception of a radio control signal.The control plane unit 350 has a preamble management unit 351 and an RAslot management unit 352.

The preamble management unit 351 manages candidates of the preamblesused in the random access, and selects the preamble used in the Msg 1during the random access to the relay station 200 or base station 100.When the preamble for the relay station and the preamble for the mobilestation are distinguished, the preamble management unit 351 selects thepreamble for the mobile station.

The RA slot management unit 352 grasps an RA slot, and selects an RAslot used to transmit the Msg 1 during the random access to the relaystation 200 or base station 100. When the RA slot for the relay stationand the RA slot for the mobile station are distinguished, the RA slotmanagement unit 352 selects the RA slot for the mobile station.

With regard to the random access, processes performed by the basestation 100, relay station 200 and mobile station 300 (or mobile station300 a) will be described below. In the second embodiment, the basestation 100 determines based on the used preamble whether a transmissionsource of the Msg 1 is the relay station or mobile station.

FIG. 9 is a flowchart illustrating a process of the base stationaccording to the second embodiment. The process illustrated in FIG. 9includes the following steps:

(Step S111) The radio communication unit 110 receives the preamble(Msg 1) through the PRACH. At this time, a transmission source of theMsg 1 is not concretely identified.

(Step S112) The preamble management unit 161 determines whether thereceived preamble is a preamble for the relay station. If so, theprocess advances to step S113. If not, the process proceeds to stepS114.

(Step S113) The backhaul controller 163 selects a DL backhaul of each ofthe relay stations 200 and 200 a within the period in which the Msg 2 istransmitted (namely, the period within A pieces of subframes after threesubframes from the subframe in which the Msg 1 is received). The processthen proceeds to step S115.

(Step S114) The control plane unit 160 performs scheduling and selectsan arbitrary subframe within the period in which the Msg 2 istransmitted.

(Step S115) The radio communication unit 110 transmits the Msg 2 throughthe PDCCH or R-PDCCH of the subframe selected at step S113 or S114. Inthe case where a plurality of subframes are selected at step S113 whentiming of the DL backhauls is different between the relay stations 200and 200 a, the radio communication unit 110 transmits the Msg 2 in eachsubframe. The reason is that whether at the time of receiving the Msg 1,any of the relay stations 200 and 200 a transmit the Msg 1 is notidentified.

(Step S116) The radio communication unit 110 receives the Msg 3.

(Step S117) The control plane unit 160 determines a transmission sourceof the Msg 3. The transmission source of the Msg 3 is determined byusing an identifier included in the Msg 3. If the transmission source isthe relay station, the process advances to step S118. If thetransmission source is not the relay station, the process proceeds tostep S119. Here, the transmission source is supposed to be the relaystation 200.

(Step S118) The backhaul controller 163 selects a DL backhaul of therelay station 200 within the period (namely, the period within B piecesof subframes counted from the subframe in which the Msg 3 is received)in which the Msg 4 is transmitted. The process then proceeds to stepS120. Since the transmission source of the Msg 3 is concretelyidentified at the time of receiving the Msg 3, the backhaul controller163 need not select a DL backhaul of the relay station 200 a.

(Step S119) The control plane unit 160 performs scheduling and selectsan arbitrary subframe within the period in which the Msg 4 istransmitted.

(Step S120) The radio communication unit 110 transmits the Msg 4 throughthe PDCCH or R-PDCCH of the subframe selected at step S118 or S119.

FIG. 10 is a flowchart illustrating a process of the relay stationaccording to the second embodiment. The process illustrated in FIG. 10includes the following steps:

(Step S121) The radio communication unit 210 receives broadcastinformation through the PBCH from the base station 100. In the broadcastinformation, information on timing of the RA slot is included. The RAslot may be shared by the relay station and the mobile station. The RAtransmission management unit 262 selects the RA slot of the UL backhaul.Note that when reception of radio signals from the mobile station 300may be stopped, the RA transmission management unit 262 may select RAslot except RA slot in the UL backhaul.

(Step S122) From among candidates of the preambles, the preamblemanagement unit 261 selects a preamble for the relay station. Thepreamble for the relay station may be shared by the relay stations 200and 200 a. The radio communication unit 210 transmits the selectedpreamble by using the RA slot selected at step S121.

(Step S123) The backhaul controller 263 limits transmission of a radiosignal (including a reference signal) to the mobile station 300 throughthe DL backhaul. When the Msg 2 is transmitted through the PDCCH, thebackhaul controller 263 stops transmitting a signal in both of the areasfor control and data. When the Msg 2 is transmitted through the R-PDCCH,the backhaul controller 263 stops transmitting a signal at least in thearea for data.

(Step S124) The radio communication unit 210 receives the Msg 2 from thebase station 100 through the PDCCH or R-PDCCH of the DL backhaul.

(Step S125) The radio communication unit 210 transmits the Msg 3 to thebase station 100. Preferably, the radio communication unit 210 transmitsthe Msg 3 to the base station 100 through the UL backhaul.

(Step S126) The backhaul controller 263 limits transmission of a radiosignal (including a reference signal) to the mobile station 300 throughthe DL backhaul. When the Msg 4 is transmitted through the PDCCH, thebackhaul controller 263 stops transmitting a signal in both of the areasfor control and data. When the Msg 4 is transmitted through the R-PDCCH,the backhaul controller 263 stops transmitting a signal at least in thearea for data.

(Step S127) The radio communication unit 210 receives the Msg 4 from thebase station 100 through the PDCCH or R-PDCCH of the DL backhaul.Through the above steps, the radio communication unit 210 completes aprocedure of random access from the relay station 200 to the basestation 100.

FIG. 11 is a flowchart illustrating a process of the mobile stationaccording to the second embodiment. Suppose here that the mobile station300 performs the random access to the relay station 200 or base station100. The process illustrated in FIG. 11 includes the following steps:

(Step S131) The radio communication unit 310 receives broadcastinformation through the PBCH from the relay station 200 or base station100. In the broadcast information, information on the timing of the RAslot is included. The RA slot management unit 352 selects one RA slot.

(Step S132) The preamble management unit 351 selects one preamble forthe mobile station from among candidates of the preambles. The radiocommunication unit 310 transmits the selected preamble through the RAslot selected at step S131.

(Step S133) The radio communication unit 310 monitors the PDCCH withinthe period (namely, the period of A pieces of subframes after threesubframes from the subframe in which the Msg 1 is transmitted) in whichthe Msg 2 is transmitted, and receives the Msg 2 from the relay station200 or base station 100. Note that the radio communication unit 310receives the Msg 2 in subframe except the subframe in DL backhaul.

(Step S134) The radio communication unit 310 transmits the Msg 3 to therelay station 200 or base station 100. The radio communication unit 310transmits the Msg 3 to the relay station 200 in subframe except thesubframe in UL backhaul.

(Step S135) The radio communication unit 310 monitors the PDCCH withinthe period (namely, the period of B pieces of subframes counted from thesubframe in which the Msg 3 is transmitted) in which the Msg 4 istransmitted, and receives the Msg 4 from the relay station 200 or basestation 100. Note that the radio communication unit 310 receives the Msg4 from the relay station 200 in subframe except the subframe in DLbackhaul.

(Step S136) Through the process up to step S135, the radio communicationunit 310 completes a procedure of the random access from its own stationto the relay station 200 or base station 100. Subsequently, the radiocommunication unit 310 performs data communication between its ownstation and any of the relay station 200 and the base station 100. Notethat when connected to the relay station 200, the mobile station 300performs data communication in subframe except the subframe in backhaul.

FIG. 12 illustrates a random access example according to the secondembodiment. The message flow illustrated in FIG. 12 includes thefollowing steps:

(Step S11) The relay station 200 transmits the Msg 1 to the base station100 through the UL backhaul. The preamble to be transmitted as the Msg 1is a preamble for the relay station. Based on the preamble, the basestation 100 recognizes that a transmission source of the Msg 1 is therelay station 200.

(Step S12) The base station 100 transmits the Msg 2 through the R-PDCCHof the DL backhaul of the relay station 200 within the period in whichthe Msg 2 is transmitted. When a signal such as a reference signal isnot transmitted in the area for data, the relay station 200 receives theMsg 2.

(Step S13) The base station 100 transmits the Msg 2 through the DLbackhaul of the relay station 200 a within the period in which the Msg 2is transmitted. Note that since the relay station 200 a did not transmitMsg 1, it ignores the Msg 2 received from the base station 100.

(Step S14) The relay station 200 transmits the Msg 3 to the base station100 through the UL backhaul. Based on an identifier included in the Msg3, the base station 100 recognizes that a transmission source of the Msg3 is the relay station 200.

(Step S15) The base station 100 transmits the Msg 4 through the R-PDCCHof the DL backhaul of the relay station 200 within the period in whichthe Msg 4 is transmitted. When a signal such as a reference signal isnot transmitted in the area for data, the relay station 200 receives theMsg 4.

In the proposed radio communication system of the second embodiment, thebase station 100 is configured to determine based on the preamblereceived as the Msg 1 whether a transmission source of the Msg 1 is therelay station or mobile station. In the case where the transmissionsource is the relay station, the base station 100 then controlstransmission timing so that the transmission source may receive the Msg2 through an existing DL backhaul. In the case where a transmissionsource of the Msg 3 is the relay station 200, the base station 100further controls transmission timing so that the relay station 200 mayreceive the Msg 4 through an existing DL backhaul. According to thesecond embodiment, the radio communication system suppressesself-interference of the relay station 200 and smoothly performs randomaccess from the relay station 200 to the base station 100.

Third Embodiment

A third embodiment will be described below. Since the third embodimentshares some elements with the foregoing second embodiment, the followingdiscussion will focus on their distinctive points, omitting explanationsof similar elements. The third embodiment differs from the secondembodiment in a method for determining whether a transmission source ofthe Msg 1 is the relay station or mobile station.

A radio communication system according to the third embodiment isdeployed by using the same apparatus configuration as that of the secondembodiment illustrated in FIG. 2. Further, a base station, a relaystation, and a mobile station according to the third embodiment aredeployed by using the same block configurations as those of the secondembodiment illustrated in FIGS. 6 to 8. Hereinafter, the thirdembodiment will be described with reference to the same referencenumerals as those illustrated in FIGS. 6 to 8.

FIG. 13 is a flowchart illustrating a process of the base stationaccording to the third embodiment. The process illustrated in FIG. 13includes the following steps:

(Step S211) The RA slot management unit 162 configures separate RA slotsfor the relay station and the mobile station. Through the PBCH, theradio communication unit 110 transmits information indicating timing ofthe RA slots for the mobile station and the relay station as broadcastinformation. Note that the radio communication unit 110 may transmitinformation indicating timing of the RA slot for the relay station asindividual control data to the relay stations 200 and 200 a.

As described in 3rd Generation Partnership Project, “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation”,3GPP TS 36.211 V9.1.0, 2010-03, normal information indicating timing ofthe RA slot is transmitted as a parameter (PRACH Configuration Index) inthe broadcast information. Suppose, for example, that the informationindicating timing of the RA slot for the relay station is inserted as anew parameter into the broadcast information for transmission. The RAslot for the relay station may be set to a low frequency such as onetime per 40 msec.

(Step S212) The radio communication unit 110 receives a preamble throughthe PRACH.

(Step S213) The RA slot management unit 162 determines whether thepreamble is received through the RA slot for the relay station or themobile station. If the preamble is received through the RA slot for therelay station, the process advances to step S214. If the preamble isreceived through the RA slot for the mobile station, the processproceeds to step S215.

(Step S214) The backhaul controller 163 selects each DL backhaul of therelay stations 200 and 200 a within the period in which the Msg 2 istransmitted. The process then proceeds to step S216.

(Step S215) The control plane unit 160 performs scheduling and selectsan arbitrary subframe within the period in which the Msg 2 istransmitted.

(Step S216) The radio communication unit 110 transmits the Msg 2 throughthe PDCCH or R-PDCCH of the subframe selected at step S214 or S215. Whenthe timing of the DL backhauls is different between the relay stations200 and 200 a, the radio communication unit 110 transmits the Msg 2through each DL backhaul.

(Step S217) The radio communication unit 110 receives the Msg 3.

(Step S218) The control plane unit 160 determines a transmission sourceof the Msg 3. If the transmission source is the relay station, theprocess advances to step S219. If the transmission source is not therelay station, the process proceeds to step S220. Here, the transmissionsource is supposed to be the relay station 200.

(Step S219) The backhaul controller 163 selects the DL backhaul of therelay station 200 within the period in which the Msg 4 is transmitted.The process then proceeds to step S221. The backhaul controller 163 neednot select the DL backhaul of the relay station 200 a.

(Step S220) The control plane unit 160 performs scheduling and selectsan arbitrary subframe within the period in which the Msg 4 istransmitted.

(Step S221) The radio communication unit 110 transmits the Msg 4 throughthe PDCCH or R-PDCCH of the subframe selected at step S219 or S220.

FIG. 14 is a flowchart illustrating a process of the relay stationaccording to the third embodiment. The process illustrated in FIG. 14includes the following steps:

(Step S231) Through the PBCH, the radio communication unit 210 receivesbroadcast information from the base station 100. In the broadcastinformation, information indicating timing of the RA slot for the relaystation is included.

(Step S232) The RA transmission management unit 262 selects the RA slotfor the relay station. The RA transmission management unit 262preferably selects the RA slot for the relay station provided on the ULbackhaul.

(Step S233) The preamble management unit 261 selects one preamble fromamong the candidates of the preambles. The candidates of the preamblesare shared by the relay stations 200 and 200 a, or by the mobilestations 300 and 300 a. The radio communication unit 210 transmits theselected preamble through the RA slot selected at step S232.

(Step S234) The backhaul controller 263 limits transmission of a radiosignal (including a reference signal) to the mobile station 300 throughthe DL backhaul.

(Step S235) The radio communication unit 210 receives the Msg 2 from thebase station 100 through the PDCCH or R-PDCCH of the subframe in DLbackhaul.

(Step S236) The radio communication unit 210 transmits the Msg 3 to thebase station 100. Preferably, the radio communication unit 210 transmitsthe Msg 3 to the base station 100 through the UL backhaul.

(Step S237) The backhaul controller 263 limits transmission of a radiosignal (including a reference signal) to the mobile station 300 throughthe DL backhaul.

(Step S238) The radio communication unit 210 receives the Msg 4 from thebase station 100 through the PDCCH or R-PDCCH of the subframe in DLbackhaul.

FIG. 15 is a flowchart illustrating a process of the mobile stationaccording to the third embodiment. Here, the mobile station 300 issupposed to perform random access to the relay station 200 or basestation 100. The process illustrated in FIG. 15 includes the followingsteps:

(Step S241) The radio communication unit 310 receives broadcastinformation from the relay station 200 or base station 100 through thePBCH. In the broadcast information, information indicating timing of theRA slot for the mobile station is included. The RA slot management unit352 selects the RA slot for the mobile station.

(Step S242) The preamble management unit 351 selects one preamble fromamong the candidates of the preambles. The candidates of the preamblesare shared by the relay stations 200 and 200 a or by the mobile stations300 and 300 a. The radio communication unit 310 transmits the selectedpreamble through the RA slot selected at step S241.

(Step S243) The radio communication unit 310 monitors the PDCCH withinthe period in which the Msg 2 is transmitted, and receives the Msg 2from the relay station 200 or base station 100. Note that the radiocommunication unit 310 receives the Msg 2 from the relay station 200through subframe except the subframe in DL backhaul.

(Step S244) The radio communication unit 310 transmits the Msg 3 to therelay station 200 or base station 100. The radio communication unit 310transmits the Msg 3 to the relay station 200 through subframe except thesubframe in UL backhaul.

(Step S245) The radio communication unit 310 monitors the PDCCH withinthe period in which the Msg 4 is transmitted, and receives the Msg 4from the relay station 200 or base station 100. Note that the radiocommunication unit 310 receives the Msg 4 from the relay station 200through subframe except the subframe in DL backhaul.

(Step S246) The radio communication unit 310 performs data communicationbetween its own station and any of the relay station 200 and the basestation 100. Note that when connected to the relay station 200, theradio communication unit 310 performs data communication throughsubframe except subframe in the backhaul.

FIG. 16 illustrates a random access example according to the thirdembodiment. The message flow illustrated in FIG. 16 includes thefollowing steps:

(Step S21) The relay station 200 transmits the Msg 1 to the base station100 through the RA slot for the relay station of the UL backhaulsubframe. The preamble transmitted as the Msg 1 may be shared by therelay station and the mobile station. Based on the reception timing ofthe preamble, the base station 100 recognizes that a transmission sourceof the Msg 1 is the relay station 200.

(Step S22) The base station 100 transmits the Msg 2 through the R-PDCCHof the DL backhaul of the relay station 200 within the period in whichthe Msg 2 is transmitted. When a signal such as a reference signal isnot transmitted in the area for data, the relay station 200 receives theMsg 2.

(Step S23) The base station 100 transmits the Msg 2 through the DLbackhaul of the relay station 200 a within the period in which the Msg 2is transmitted.

(Step S24) The relay station 200 transmits the Msg 3 to the base station100 through the UL backhaul. Based on the identifier included in the Msg3, the base station 100 recognizes that a transmission source of the Msg3 is the relay station 200.

(Step S25) The base station 100 transmits the Msg 4 through the R-PDCCHof the DL backhaul of the relay station 200 within the period in whichthe Msg 4 is transmitted. When a signal such as a reference signal isnot transmitted in the area for data, the relay station 200 receives theMsg 4.

Incidentally, the base station 100 need not always configure the RA slotfor the relay station. Specifically, the base station 100 may configurethe RA slot after detecting the RA trigger about the relay stations 200and 200 a.

FIG. 17 illustrates another random access example according to the thirdembodiment. The base station 100 does not allocate a radio resource tothe PRACH for the relay station in normal situation. On the other hand,when detecting an RA trigger and determining that any of the relaystations 200 and 200 a may perform random access, the base station 100allocates a radio resource to the PRACH for the relay station. At thistime, by using a timer, the base station 100 may limit a period in whicha radio resource is allocated. The relay stations 200 and 200 a transmitthe Msg 1 within the period. As can be seen from the above discussion,when the relay stations 200 and 200 a do not perform random access, thebase station 100 allocates a radio resource of the RA slot used for therelay station to arbitrary channel except the PRACH, thus making use ofa radio resource efficient.

According to the third embodiment, the proposed radio communicationsystem permits the base station 100 to determine, based on the timing atwhich the Msg 1 is received, whether a transmission source of the Msg 1is the relay station or mobile station. When the transmission source isthe relay station, the base station 100 then controls transmissiontiming so that the relay station may receive the Msg 2 through anexisting DL backhaul. When the transmission source of the Msg 3 is therelay station 200, the base station 100 further controls transmissiontiming so that the relay station 200 may receive the Msg 4 through anexisting DL backhaul. According to the third embodiment, the radiocommunication system suppresses self-interference of the relay station200 and smoothly performs random access from the relay station 200 tothe base station 100.

Fourth Embodiment

A fourth embodiment will be described below. Since the fourth embodimentshares some elements with the foregoing second and third embodiments,the following discussion will focus on their distinctive points,omitting explanations of similar elements. The fourth embodiment differsfrom the second and third embodiments in timing at which the Msg 2 or 4is transmitted.

A radio communication system according to the fourth embodiment isdeployed by using the same apparatus configuration as that of the secondembodiment illustrated in FIG. 2. Further, a base station, a relaystation, and a mobile station according to the fourth embodiment aredeployed by using the same block configurations as those of the secondembodiment illustrated in FIGS. 6 to 8. Hereinafter, the fourthembodiment will be described with reference to the same referencenumerals as those illustrated in FIGS. 6 to 8.

FIG. 18 is a flowchart illustrating a process of the base stationaccording to the fourth embodiment. Since processes of steps S311, S312,S314 to S317, S319, and S320 illustrated in FIG. 18 are the same asthose of steps S111, S112, S114 to S117, S119, and S120 illustrated inFIG. 9, a description will not be repeated.

(Step S313) The backhaul controller 163 selects the DL default backhaulwithin the period in which the Msg 2 is transmitted. The defaultbackhaul is a backhaul which is not effective in normal situation butautomatically becomes effective at the time of the random access. Thetiming of the default backhaul is, for example, mutually configuredbetween the relay stations 200 and 200 a. The timing of the defaultbackhaul of the relay stations 200 and 200 a is previously configuredbetween their own stations and the base station 100, and is configured,for example, by a telecommunications operator at the time of deployingthe relay stations 200 and 200 a.

(Step S318) The backhaul controller 163 selects the DL default backhaulwithin the period in which the Msg 4 is transmitted.

FIG. 19 is a flowchart illustrating a process of the relay stationaccording to the fourth embodiment. The process illustrated in FIG. 19includes the following steps:

(Step S321) The control plane unit 260 determines whether to detect theRA trigger. If so, the process proceeds to step S322. If not, thecontrol plane unit 260 repeats a process of step S321.

(Step S322) In addition to an existing backhaul, the backhaul controller263 makes the default backhaul with predetermined timing effective.

(Step S323) The RA transmission management unit 262 selects an RA slotof the UL default backhaul subframe. Note that when stopping receiving aradio signal from the mobile station 300, the RA transmission managementunit 262 may select RA slot except that of the UL default backhaul.

(Step S324) From among the candidates of the preambles, the preamblemanagement unit 261 selects the preamble for the relay station. Theradio communication unit 210 transmits the selected preamble through theRA slot selected at step S323.

(Step S325) In addition to the DL backhaul, the backhaul controller 263limits transmission of a radio signal to the mobile station 300 throughthe DL default backhaul.

(Step S326) The radio communication unit 210 receives the Msg 2 from thebase station 100 through the PDCCH or R-PDCCH of the DL defaultbackhaul.

(Step S327) The radio communication unit 210 transmits the Msg 3 to thebase station 100. Preferably, the radio communication unit 210 transmitsthe Msg 3 to the base station 100 through the UL default backhaul.

(Step S328) In addition to the DL backhaul, the backhaul controller 263limits transmission of a radio signal to the mobile station 300 throughthe DL default backhaul.

(Step S329) The radio communication unit 210 receives the Msg 4 from thebase station 100 through the PDCCH or R-PDCCH of the DL defaultbackhaul.

FIG. 20 illustrates a random access example according to the fourthembodiment. The message flow illustrated in FIG. 20 includes thefollowing steps:

(Step S31) The relay station 200 transmits the Msg 1 to the base station100 through the UL default backhaul. The preamble to be transmitted is apreamble for the relay station. Based on the preamble, the base station100 recognizes that a transmission source of the Msg 1 is the relaystation.

(Step S32) The base station 100 transmits the Msg 2 through the R-PDCCHof the DL default backhaul within the period in which the Msg 2 istransmitted. The base station 100 need not transmit the Msg 2 througheach DL backhaul of the relay stations 200 and 200 a. When a signal suchas a reference signal is not transmitted in the area for data, the relaystation 200 receives the Msg 2. When the default backhaul is validated,the relay station 200 a receives the Msg 2, whereas when the defaultbackhaul is not validated, the relay station 200 a does not receive theMsg 2.

(Step S33) The relay station 200 transmits the Msg 3 to the base station100 through the UL default backhaul. Based on the identifier included inthe Msg 3, the base station 100 recognizes that a transmission source ofthe Msg 3 is the relay station 200.

(Step S34) The base station 100 transmits the Msg 4 through the R-PDCCHof the DL default backhaul within the period in which the Msg 4 istransmitted. When a signal such as a reference signal is not transmittedin the area for data, the relay station 200 receives the Msg 4.

In the foregoing description, whether a transmission source of the Msg 1is the relay station is determined by using a method according to thesecond embodiment. Further, determination may be performed by using amethod according to the third embodiment.

FIG. 21 illustrates another random access example according to thefourth embodiment. The message flow illustrated in FIG. 21 includes thefollowing steps:

(Step S35) The relay station 200 transmits the Msg 1 to the base station100 through the RA slot for the relay station of the UL default backhaulsubframe. Based on the reception timing of the preamble, the basestation 100 recognizes that a transmission source of the Msg 1 is therelay station. After detecting the RA trigger, the base station 100 maymake the RA slot for the relay station validated.

(Step S36) The base station 100 transmits the Msg 2 through the R-PDCCHof the DL default backhaul within the period in which the Msg 2 istransmitted. When a signal such as a reference signal is not transmittedin the area for data, the relay station 200 receives the Msg 2.

(Step S37) The relay station 200 transmits the Msg 3 to the base station100 through the UL default backhaul. Based on an identifier included inthe Msg 3, the base station 100 recognizes that a transmission source ofthe Msg 3 is the relay station 200.

(Step S38) The base station 100 transmits the Msg 4 through the R-PDCCHof the DL default backhaul within the period in which the Msg 4 istransmitted. When a signal such as a reference signal is not transmittedin the area for data, the relay station 200 receives the Msg 4.

In the fourth embodiment, in the same manner as in the second and thirdembodiments, the proposed radio communication system smoothly performsrandom access from the relay station 200 to the base station 100.Further, in the fourth embodiment, the radio communication system makescommon transmission timing of the Msg 2 and Msg 4, and simplifiescontrol of random access. A point that the transmission timing is madeto be common is particularly validated in the case of random accessinvolved in a handover.

Fifth Embodiment

A fifth embodiment will be described below. Since the fifth embodimentshares some elements with the foregoing second and third embodiments,the following discussion will focus on their distinctive points,omitting explanations of similar elements. The fifth embodiment differsfrom the second and third embodiments in a subframe in which an RA slotis configured.

A radio communication system according to the fifth embodiment isdeployed by using the same apparatus configuration as that of the secondembodiment illustrated in FIG. 2. Further, a base station, a relaystation, and a mobile station according to the fifth embodiment aredeployed by using the same block configurations as those of the secondembodiment illustrated in FIGS. 6 to 8. Hereinafter, the fifthembodiment will be described with reference to the same referencenumerals as those illustrated in FIGS. 6 to 8.

FIG. 22 is a flowchart illustrating a process of the base stationaccording to the fifth embodiment. Since processes of steps S412, S413,and S415 to S421 illustrated in FIG. 22 are the same as those of stepsS212, S213, and S215 to S221 illustrated in FIG. 13, a description willnot be repeated.

(Step S411) The RA slot management unit 162 configures an RA slot forthe relay station in a subframe before k pieces of subframes (e.g.,three subframes) from the DL backhaul of the relay stations 200 and 200a. When timing of the DL backhauls is different between the relaystations 200 and 200 a, the RA slot management unit 162 configures theRA slot for the relay station before k pieces of subframes from each DLbackhaul.

(Step S414) The backhaul controller 163 selects a DL backhaul after kpieces of subframes from the subframe in which the Msg 1 is received.Note that when there are circumstances that the Msg 2 cannot betransmitted from a subframe after k pieces of subframes from the abovesubframe, the backhaul controller 163 may select another DL backhaulafter k pieces of subframes or later from the above subframe within theperiod in which the Msg 2 is transmitted.

FIG. 23 is a flowchart illustrating a process of the relay stationaccording to the fifth embodiment. Since processes of steps S432, S433,and S435 to S437 illustrated in FIG. 23 are the same as those of stepsS233, S234, and S236 to S238 illustrated in FIG. 14, a description willnot be repeated.

(Step S431) The RA transmission management unit 262 selects an RA slotof a subframe before k pieces of subframes (e.g., three subframes) fromthe DL backhaul as the RA slot for the relay station. When a subframe ofthe selected RA slot is not an UL backhaul subframe, the backhaulcontroller 263 controls that data not to be received from the mobilestation 300 through the subframe.

(Step S434) The radio communication unit 210 starts monitoring the PDCCHor R-PDCCH from the DL backhaul subframe after k pieces of subframesfrom the subframe in which the Msg 1 is transmitted. The Msg 2 isexpected to be received through the DL backhaul. Note that when the Msg2 is not received through the DL backhaul, the radio communication unit210 monitors the PDCCH or R-PDCCH from the DL backhaul subframe afterthe above subframes or later.

FIG. 24 illustrates a random access example according to the fifthembodiment. The message flow illustrated in FIG. 24 includes thefollowing steps:

(Step S41) The relay station 200 transmits the Msg 1 to the base station100 through the RA slot of a subframe before three subframes from the DLbackhaul subframe. Based on the reception timing of the preamble, thebase station 100 recognizes that a transmission source of the Msg 1 isthe relay station.

(Step S42) The base station 100 transmits the Msg 2 through the R-PDCCHof the DL backhaul subframe after three subframes from the subframe inwhich the Msg 1 is received. When a signal such as a reference signal isnot transmitted in the area for data, the relay station 200 receives theMsg 2.

(Step S43) The relay station 200 transmits the Msg 3 to the base station100 through the UL backhaul. Based on the identifier included in the Msg3, the base station 100 recognizes that a transmission source of the Msg3 is the relay station 200.

(Step S44) The base station 100 transmits the Msg 4 through the R-PDCCHof the DL backhaul of the relay station 200 within the period in whichthe Msg 4 is transmitted. When a signal such as a reference signal isnot transmitted in the area for data, the relay station 200 receives theMsg 4.

In the foregoing description, whether a transmission source of the Msg 1is the relay station is determined by using a method according to thethird embodiment; further, may be determined by using a method accordingto the second embodiment.

In the fifth embodiment, in the same manner as in the second and thirdembodiments, the proposed radio communication system smoothly performsrandom access from the relay station 200 to the base station 100.Further, in the fifth embodiment, the relay station 200 smoothly startsrandom access even if an RA slot is not provided on the UL backhaul. Inaddition, the relay station 200 preferably monitors a reception signalafter predetermined time after transmitting the Msg 1, thus simplifyingcontrol.

Sixth Embodiment

A sixth embodiment will be described below. Since the sixth embodimentshares some elements with the foregoing second and third embodiments,the following discussion will focus on their distinctive points,omitting explanations of similar elements. In the sixth embodiment, theMsg 2 and Msg 4 are transmitted also through subframe except thesubframe in DL backhaul of the relay station.

A radio communication system according to the sixth embodiment isdeployed by using the same apparatus configuration as that of the secondembodiment illustrated in FIG. 2. Further, a base station, a relaystation, and a mobile station according to the sixth embodiment aredeployed by using the same block configurations as those of the secondembodiment illustrated in FIGS. 6 to 8. Hereinafter, the sixthembodiment will be described with reference to the same referencenumerals as those illustrated in FIGS. 6 to 8.

FIG. 25 is a flowchart illustrating a process of the base stationaccording to the sixth embodiment. Since processes of steps S511, S512,S514 to S517, S519, and S520 illustrated in FIG. 25 are the same asthose of steps S111, S112, S114 to S117, S119, and S120 illustrated inFIG. 9, a description will not be repeated.

(Step S513) The backhaul controller 163 selects a subframe after mpieces of subframes from the subframe in which the Msg 1 is received. Acharacter m indicates a predetermined value of the base station 100 andthe relay stations 200 and 200 a, and is set, for example, to be equalto three.

(Step S518) The backhaul controller 163 selects a subframe after npieces of subframes from the subframe in which the Msg 3 is received. Acharacter n indicates a predetermined value of the base station 100 andthe relay stations 200 and 200 a, and is set, for example, to be equalto eight.

FIG. 26 is a flowchart illustrating a process of the relay stationaccording to the sixth embodiment. Since processes of steps S521, S522,and S525 illustrated in FIG. 26 are the same as those of steps S121,S122, and S125 illustrated in FIG. 10, a description will not berepeated.

(Step S523) The backhaul controller 263 limits transmission of a radiosignal (including a reference signal) to the mobile station 300 througha subframe after m pieces of subframes from the subframe in which theMsg 1 is transmitted. When the Msg 2 is transmitted through the PDCCH,the backhaul controller 263 stops transmitting a signal in both of theareas for control and data. When the Msg 2 is transmitted through theR-PDCCH, the backhaul controller 263 stops transmitting a signal atleast in the area for data.

(Step S524) The radio communication unit 210 receives the Msg 2 from thebase station 100 through the PDCCH or R-PDCCH of a subframe after the mpieces of subframes from the above subframe.

(Step S526) The backhaul controller 263 limits transmission of a radiosignal (including a reference signal) to the mobile station 300 througha subframe after n pieces of subframes from the subframe in which theMsg 3 is transmitted. When the Msg 4 is transmitted through the PDCCH,the backhaul controller 263 stops transmitting a signal in both of theareas for control and data. When the Msg 4 is transmitted through theR-PDCCH, the backhaul controller 263 stops transmitting a signal atleast in the area for data.

(Step S527) The radio communication unit 210 receives the Msg 4 from thebase station 100 through the PDCCH or R-PDCCH of a subframe after the npieces of subframes from the above subframe.

FIG. 27 illustrates a random access example according to the sixthembodiment. The message flow illustrated in FIG. 27 includes thefollowing steps:

(Step S51) The relay station 200 transmits the Msg 1 to the base station100 by using a preamble for the relay station. Based on the preamble,the base station 100 recognizes that a transmission source of the Msg 1is the relay station.

(Step S52) The base station 100 transmits the Msg 2 through the R-PDCCHof a subframe after three subframes from the subframe in which the Msg 1is received. Through a subframe after three subframes of the subframe inwhich the Msg 1 is transmitted, the relay station 200 controls a signalsuch as a reference signal not to be transmitted in the area for data,thus receiving the Msg 2.

(Step S53) The relay station 200 transmits the Msg 3 to the base station100. Based on the identifier included in the Msg 3, the base station 100recognizes that a transmission source of the Msg 3 is the relay station200.

(Step S54) Through the R-PDCCH of a subframe after eight subframes fromthe subframe in which the Msg 3 is received, the base station 100transmits the Msg 4. Through a subframe after eight subframes from thesubframe in which the Msg 3 is transmitted, the relay station 200controls a signal such as a reference signal not to be transmitted inthe area for data, thus receiving the Msg 4.

In the foregoing description, whether a transmission source of the Msg 1is the relay station is determined by using a method according to thesecond embodiment; further, may be determined by using a methodaccording to the third embodiment.

In the sixth embodiment, in the same manner as in the second and thirdembodiments, the proposed radio communication system smoothly performsrandom access from the relay station 200 to the base station 100. In thesixth embodiment, since an interval between the Msg 1 and Msg 2 as wellas the interval between the Msg 3 and Msg 4 is fixed, the radiocommunication system simplifies control of random access in the relaystation 200. On the other hand, about the random access from the mobilestation 300 a to the base station 100, since the intervals are notfixed, the radio communication system secures flexibility of scheduling.

Seventh Embodiment

A seventh embodiment will be described below. Since the seventhembodiment shares some elements with the foregoing second embodiment,the following discussion will focus on their distinctive points,omitting explanations of similar elements. In the foregoing second tosixth embodiments, transmission timing of the Msg 2 or Msg 4 is changedbased on the fact that a transmission source of the Msg 1 or Msg 3 isthe relay station or mobile station. As compared with the above, in theseventh embodiment, even if the base station does not distinguish that atransmission source is the relay station or the mobile station, theradio communication system performs random access.

A radio communication system according to the seventh embodiment isdeployed by using the same apparatus configuration as that of the secondembodiment illustrated in FIG. 2. Further, a base station, a relaystation, and a mobile station according to the seventh embodiment aredeployed by using the same block configurations as those of the secondembodiment illustrated in FIGS. 6 to 8. Hereinafter, the seventhembodiment will be described with reference to the same referencenumerals as those illustrated in FIGS. 6 to 8.

FIG. 28 is a flowchart illustrating a process of the base stationaccording to the seventh embodiment. The process illustrated in FIG. 28includes the following steps:

(Step S611) The radio communication unit 110 receives a preamble (Msg 1)through the PRACH. At this time, a transmission source of the Msg 1 isnot concretely identified.

(Step S612) The control plane unit 160 performs scheduling, and selectsan arbitrary subframe within the period in which the Msg 2 istransmitted.

(Step S613) The radio communication unit 110 transmits the Msg 2 throughthe PDCCH or R-PDCCH of the subframe selected at step S612.

(Step S614) The radio communication unit 110 receives the Msg 3. Here,the transmission source is supposed to be the relay station 200.

(Step S615) The control plane unit 160 performs scheduling and selectsan arbitrary subframe within the period in which the Msg 4 istransmitted.

(Step S616) The radio communication unit 110 transmits the Msg 4 throughthe PDCCH or R-PDCCH of the subframe selected at step S615.

FIG. 29 is a flowchart illustrating a process of the relay stationaccording to the seventh embodiment. The process illustrated in FIG. 29includes the following steps:

(Step S621) The radio communication unit 210 receives broadcastinformation from the base station 100 through the PBCH. In the broadcastinformation, information on the timing of the RA slot is included. TheRA transmission management unit 262 selects one RA slot. The backhaulcontroller 263 controls data not to be received from the mobile station300 through the subframe on which the RA slot is provided.

(Step S622) The preamble management unit 261 selects one preamble fromamong candidates of the preambles. The radio communication unit 210transmits the selected preamble through the RA slot selected at stepS621.

(Step S623) The backhaul controller 263 limits transmission of a radiosignal (including a reference signal) to the mobile station 300 untilreceiving the Msg 2 from a head of the period in which the Msg 2 may bereceived. When the Msg 2 is transmitted through the PDCCH, the backhaulcontroller 263 stops transmitting a signal in both of the areas forcontrol and data. When the Msg 2 is transmitted through the R-PDCCH, thebackhaul controller 263 stops transmitting a signal at least in the areafor data.

(Step S624) The radio communication unit 210 receives the Msg 2 from thebase station 100 through the PDCCH or R-PDCCH.

(Step S625) The backhaul controller 263 restarts transmission of a radiosignal (including a reference signal) to the mobile station 300.

(Step S626) The radio communication unit 210 transmits the Msg 3 to thebase station 100.

(Step S627) The backhaul controller 263 limits transmission of a radiosignal (including a reference signal) to the mobile station 300 untilreceiving the Msg 4 from a head of the period in which the Msg 4 may bereceived. When the Msg 2 is transmitted through the PDCCH, the backhaulcontroller 263 stops transmitting a signal in both of the areas forcontrol and data. When the Msg 2 is transmitted through the R-PDCCH, thebackhaul controller 263 stops transmitting a signal at least in the areafor data.

(Step S628) The radio communication unit 210 receives the Msg 2 from thebase station 100 through the PDCCH or R-PDCCH.

(Step S629) The backhaul controller 263 restarts transmission of a radiosignal (including a reference signal) to the mobile station 300.

FIG. 30 illustrates a random access example according to the seventhembodiment. The message flow illustrated in FIG. 30 includes thefollowing steps:

(Step S61) The relay station 200 transmits the Msg 1 to the base station100.

(Step S62) The base station 100 performs scheduling, and transmits theMsg 2 through the R-PDCCH of any subframe within the period in which theMsg 2 is transmitted. Through a subframe after three subframes or laterfrom the subframe in which the Msg 1 is transmitted, the relay station200 controls a signal such as a reference signal not to be transmittedin the area for data, thus receiving the Msg 2.

(Step S63) The relay station 200 transmits the Msg 3 to the base station100. Based on the identifier included in the Msg 3, the base station 100recognizes that a transmission source of the Msg 3 is the relay station200.

(Step S64) The base station 100 performs scheduling, and transmits theMsg 4 through the R-PDCCH of any subframe within the period in which theMsg 4 is transmitted. Through the subframe or later in which the Msg 3is transmitted, the relay station 200 controls a signal such as areference signal not to be transmitted in the area for data, thusreceiving the Msg 4.

In the seventh embodiment, the proposed radio communication systemsuppresses self-interference of the relay station 200 and smoothlyperforms random access from the relay station 200 to the base station100. Further, the base station 100 does not distinguish random accessthrough the relay station 200 and random access through the mobilestation 300 a, and therefore preferably performs a common procedure. Asa result, the radio communication system simplifies control of therandom access.

According to the above-described radio communication system, basestation, relay station, and radio communication method, random accessthrough the relay station is smoothly performed.

All examples and conditional language provided herein are intended forthe pedagogical purposes of aiding the reader in understanding theinvention and the concepts contributed by the inventor to further theart, and are not to be construed as limitations to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although one or more embodiments of thepresent invention have been described in detail, it should be understoodthat various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

What is claimed is:
 1. A base station which is able to perform radiocommunications with a relay station and a mobile station, the basestation comprising: a transmitter configured to transmit radio signalsto the relay station in downlink backhaul subframes, and to limittransmission of radio signals to the relay station in subframes otherthan the downlink backhaul subframes; and a controller configured toallow, when performing a random access procedure to the relay station,the transmitter to transmit a message of the random access procedureeven in the subframes other than the downlink backhaul subframes.
 2. Aradio communication system comprising: a relay station; a mobilestation; and a base station which is able to perform radiocommunications with the relay station and the mobile station, the basestation including: a transmitter configured to transmit radio signals tothe relay station in downlink backhaul subframes, and to limittransmission of radio signals to the relay station in subframes otherthan the downlink backhaul subframes; and a controller configured toallow, when performing a random access procedure to the relay station,the transmitter to transmit a message of the random access procedureeven in the subframes other than the downlink backhaul subframes.